Now imagine that for the last five years the owner has been using RootX on an annual basis and he hasn't had any problem with blockages or gurgling toilets. Obviously he doesn't know if the RootX is keeping the roots at bay or if they just stopped entering the pipe for some reason. The only way he would know for sure is if he stopped using the RootX and waited a couple of years to see if they came back. That's not something he's willing to test. The minor inconvenience of using RootX once a year gives him peace of mind.
Finally, fast forward into the future and imagine the owner putting the house on the market 5, 10, maybe 15 years from now. Does he have to disclose that 10, 15, or even 20 years ago (depending on when he puts the house on the market) he used to get roots in the pipe? Does he have to disclose that he uses RootX once a year as a "peace of mind" exercise?